Nonlinear cross-polarization interactions in photonic devices and systems (POLARIZON)

Nonlinear polarization interactions among different light waves represent a fundamental physical phenomenon which is the optical analogue of atomic spin interactions in ferromagnetic materials. Our project is thus devoted to exploring the theoretical aspects and the industrial applications of polarization cross-interactions among different optical signals propagating in both deterministic and random nonlinear optical media. We will restrict our attention to the particular but immensely relevant practical case of beam interactions in nonlinear optical fibers, which provide the pipelines of today’s core telecommunications networks. The basic building block of our study will be the analysis of two-beam polarization interactions. We will consider counter-propagating waves in single-mode fibers with either same or different carrier frequencies, and co-propagating channels with different frequencies. Next we will move to study the nonlinear polarization interactions of multiple wavelength channels in wavelength-division-multiplexed (WDM) transmissions. We shall analyse the interactions among continuous waves and/or amplitude/differential phase modulated channels for bit rates up to 10 Gbit/s propagating over long-haul distances in a re-circulating fiber loop.
The main objectives of our investigations are the following. First, determining the stable, least energy mutual polarization arrangements of the waves or ground states of the coupled polarization system. These arrangements represent the asymptotic evolution of the ensemble of polarization states in the absence of external forcing. By coupling information signals to the interacting channels, we intend to generate polarization domain walls, which represent a switching of polarization among energy-equivalent, orthogonally polarized domain ground states. Polarization domain walls are topological solitons of the kink type: we also intend to explore and demonstrate the generation of polarization spin waves and their interaction/collision with the domain walls.
A practical important consequence of the absolute stability of polarization domains is the polarization attraction phenomenon, whereby the state of polarization of an initially depolarized probe beam is attracted, with no energy loss, to the same state of polarization of a pump wave. We will investigate novel device applications such as the implementation of loss-free nonlinear polarizers and Raman amplifiers enhanced by cross-phase modulation-induced polarization attraction, as well as system consequences for the stabilization of polarization modulated or polarization multiplexed WDM transmissions. For analysing long distance fiber links we will extend our analytical, numerical and experimental studies to randomly birefringent fibers, and investigate how the nonlinear cross-polarization interactions may enhance or mitigate the impact of polarization mode dispersion in WDM transmissions. In the case of dense or ultra-dense WDM transmissions, our aim is to explore and unveil novel collective dynamical behaviours for the polarization states of the comb of channels.